Power operated lift chairs are useful for raising persons, especially those having impaired mobility, from a seated to a standing position. These chairs include a powered lift mechanism which raises and tilts the chair allowing a seated occupant to stand with a limited amount of exertion. Further, in a reverse mode, the seat may lower a user from a standing to a seated position. U.S. Pat. Nos. 4,007,960, 4,083,599, and 4,993,777 describe various known lift chairs.
Lift chairs of the type known in the art typically include a base frame which rests on the floor, a mechanism attached to the base frame, an electric motor-driven actuator for motivating the mechanism, and a seating portion for receiving a user. When the lift chair is raised, a gap is formed between the seating portion and the base frame. This gap poses a risk to a pet, a small child, or an unwary adult that may wander between the seating portion and the base frame. Injury may be caused when the lift chair is adjusted from a raised to a lowered position causing the person or pet to be compressed between chair components.
It is known to use ribbon sensing switches under a seating portion or on a base frame of a lift chair, whereby a foreign object under the seating portion may contact one of the sensing switches cutting power off to a mechanism actuator. This configuration may not provide an adequate solution to the problem of protecting humans or animals that move into a position beneath a lift chair. It is possible for a human or animal to avoid contact with the sensing switches and become injured by the moving mechanism, because it is impractical to provide such a ribbon sensing switch on every potentially dangerous portion of the lift chair. Further, since many types of sensing switches require contact with an object before motion of the mechanism can be stopped, a living being may become injured trying to escape the moving lift chair or become trapped after the motion of the mechanism is stopped.
It has also been suggested that light sensors be used to sense a foreign object under a lift chair. However, this solution fails to address some of the problems in a practical and effective manner. Light sensors require a light transmitter and a light receiver which detects changes in the transmitted light. Since the size and shape of an area under a seating portion of a lift chair changes significantly during a raising or lowering operation, a sophisticated and expensive controller may be required to prevent false detection of a foreign object. Moreover, the quantity of receivers and/or transmitters that are potentially required to cover an entire area under the seating portion of a lift chair is impractical and cost prohibitive.
It would be desirable to provide an effective, practical and cost effective system which prevents injury of a living being which enters beneath a seating portion of a lift chair.